1. Field of the Invention
The present invention generally relates to a sliding exhaust brake system which is connected to the exhaust pipe of a large-sized vehicle such as a truck or bus and closes off the exhaust gas discharge passage in the exhaust pipe to brake the vehicle when it goes down a steep hill. More particularly, the invention relates to improvements in the structure of the auxiliary valve member included in such a sliding exhaust brake system.
2. Description of the Prior Art
The structure of one known auxiliary valve member used in an exhaust brake system of this kind is shown in FIG. 16, where a valve member 23 takes the form of a flat plate and is provided with a hole 24 for adjusting the exhaust pressure. An auxiliary valve member 30 consists of a liner 29 sliding on the surface of the valve member 30 together with a support frame 28 that supports the liner, The auxiliary valve member 30 is connected with the front end of a piston rod 26 of an actuator such as an air cylinder device or diaphragm device via a block member 25. Thus, the auxiliary valve member 30 can move with the flat valve member 23 after the auxiliary valve member 30 moves a given distance relative to the flat valve member 23. The passage is closed off after the exhaust pressure-adjusting hole 24 is closed by the auxiliary valve member 30. The passage is opened after the adjusting hole 24 is opened.
The structure of another known auxiliary valve member used in an exhaust brake system of this kind is shown in FIG. 17, where a valve member 23 taking the form of a flat plate forms a valve mechanism. A plurality of holes 24, 24', etc. are formed in the bottom surface of the valve member 23 to adjust the exhaust pressure. An auxiliary valve member 27 is mounted on the flat valve member 23 and designed to slide on the surface of the valve member 23. The auxiliary valve member 27 is connected with a piston rod 26 together with the flat valve member 23. A block member 25 is fixed at the front end of the rod 26. The auxiliary valve member 27 can move with the flat valve member 23 after the auxiliary valve member 27 moves a given distance relative to the flat valve member 23 while engaging the block member 25. Holes 28, 28' are formed in the auxiliary valve member 27. When the passage is closed, the exhaust pressure-adjusting holes 24, 24', etc. are closed by the auxiliary valve member 27 in the same way as in the structure described first. The passage is closed after the holes 24, 24' are opened.
In recent years, the output powers of internal combustion engines of automobiles have been increased more and more, and an increasing number of engines are supercharged. That is, engines have tended to be rotated at higher speeds. Therefore, the present situation is that the exhaust pressure and the amount of exhaust gas tend to be increased. With any of the conventional mechanisms described above, however, since the exhaust pressure increases, the obtained smoothness, especially responsiveness, tends to be insufficient especially when the exhaust passage is closed. In particular, in order to close off the passage, the exhaust pressure-adjusting hole 24 or holes 24, 24', etc. are first closed. Under this condition, the valve member 23 is moved to close off the exhaust passage. As a result, the aforementioned undesirable phenomena tend to occur. To avoid these problems, the actuator has had to be made larger.